ES2349505T3 - METHOD AND NODE FOR THE CONTROL OF A CONNECTION IN A COMMUNICATION NETWORK. - Google Patents

Abstract

In a method for the control of a connection in a communication network comprising a plurality of nodes (MSC, TSN, MG), a connection (CO) is established stepwise between nodes (MSC, TSN, MG). At least two of the nodes (MSC, TSN, MG) are adapted to insert an entity into the connection (CO), the entity affecting the connection quality, or to remove an entity affecting the connection quality from the connection. An indicator is forwarded between nodes controlling the connection (CO) wherein the indicator indicates whether the connection (CO) comprises an entity affecting the connection quality. A node which decides to insert an entity into the connection or remove an entity adjusts the indicator accordingly before forwarding it to a further node (MSC, TSN, MSC') controlling the connection (CO). A node (MSC, TSN, MSC') controlling the connection (CO) checks the value of the indicator when it performs a decision to insert or remove an entity. Nodes and program units for performing the method are also described. <IMAGE>

Description

Technical Field of the Invention

The present invention relates to a method according to the preamble of claim 1. Software devices and programs that perform the invention are also described.

Background

Communication networks consist of interconnected nodes and can be subdivided into core networks and access networks. Core networks interconnect access networks and other networks, for example other core networks or the Internet. In the UMTS architecture, an access network can be controlled by an RNC (radio network controller) that is connected to the core network and provides access to the core network, that is, it serves the node of access.

For transmission on a connection, the conversation is coded according to a coding scheme, alternatively denoted as codec. An encoding scheme can carry conversation either in a compressed mode or in an uncompressed mode. In many networks, different coding schemes can be used and different nodes may have different capabilities for handling coding schemes. The transcoders carry out transcoding and speed adaptations between different coding schemes. The TFO (Tandem Free Operation) is a configuration of two transcoders with compatible coding schemes on the voice sides compressed at the two ends of a connection, that is, in the interface with the user equipment. In this case, the transcoding steps can be avoided and compressed voice coding can be used end to end of the connection.

Out-of-band coding negotiation allows end-to-end conversation connections to be established with a common coding scheme, that is, the same conversation coding is used throughout the connection between access networks. The advantage is that keeping the voice compressed saves bandwidth in the core network and optimizes the quality of the conversation because transcoding stages are avoided.

The ITU (International Telecommunication Union) protocol BICC (bearer independent call control) supports out-of-band signaling procedures that allow negotiation of the coding scheme between access nodes. In the ITU-T proposal BIC Q.1901 (International Telecommunication Union, June 2000), the negotiation of the coding schemes is carried out from the start control node in a connection to each subsequent node including a list of schemes coding allowed in the APP parameter (Application Transport Parameter) in the IAM (Initial Addess Message) for connection establishment. Each node checks the list and if it does not support a particular type of coding it removes it from the list. The adapted list is communicated with the IAM and unsupported types are removed as long as BICC signaling is supported. When the final node is reached, either the termination node or the last node that supports BICC, the type of coding scheme with the highest priority is selected. This coding scheme and the list (reduced to a list of active coding schemes) are returned to the start node through all intermediate nodes.

If a node carries out a transcoder selection at one edge of the PLMN (Public Land Mobile Network) then the indication of the selected coding scheme to subsequent nodes in the connection section through the PLM network is a compressed voice coding scheme. In the BICC coding scheme negotiation procedures there are no rules that define how many transcoding stages are allowed and if an access network that supports an out-of-band coding scheme negotiation can insert transcoders to maintain TrFO (transcoder free operation - operation without transcoders) between the access node and the rest of the network. The number of transcoding stages in an end-to-end connection can seriously affect the quality of the conversation. If TFO is not possible, more than three transcoding steps typically cause substantial conversation degradation. The number of stages that cause substantial degradation depends on the coding algorithm and the degradation of the conversation by other entities of the connection.

The negotiation procedures of the coding scheme can cause transcoders to be inserted to allow supplementary services or because carrier technology in a node or network does not support compressed voice. For example, ATM (Asynchronous Transfer Mode) networks allow the transmission of either compressed or uncompressed conversation while STM (Synchronous Transfer Mode) networks require uncompressed conversation coding. In addition, negotiation would result in the optimal situation of transcoders, which is not always the case. For example, for connections that leave an STM network to ATM, a transcoder should be placed on the edge of the network to save bandwidth in the ATM network by using a compressed coding scheme.

In many cases, it is necessary to modify the coding scheme in a section of a connection. For example, a connection is often transferred between different access networks due to a delivery. Modifications in the core network are disadvantageous, especially if they require a higher transmission bandwidth that will often not be available causing termination of the connection. The number of transcoders in a connection can be increased by a modification with the corresponding degradation of quality. Again, an optimal transcoder situation is often not achieved.

US 6,903,862 describes a method and apparatus for the detection of tandem voice coding to modify the filtering of the voice encoder in order to avoid a degradation of the conversation due to the tandem voice coding operation in A digital communication system. In the method a voice encoder passes PCM signals to a Public Switched Telephone Network (PSTN) and receives PCM inputs over the PSTN. The voice encoder adds a detection code to the output and constantly monitors the least significant bit of the PCM input for a detection code indicating that a second voice encoder is connected at the receiving end. If the detection code is detected, then a modified filter mode is established. In the modified filter mode, the filtering is modified to prevent degradation of the outgoing conversation signals. However, this patent does not solve the above problems.

Summary and description of the invention

An object of the present invention is to obviate the above disadvantages and

5 improve the average quality of connections in a communication network. Another object is to avoid both the deterioration of a connection due to changes in the coding scheme and to minimize impacts on the connection in the core network.

In accordance with the invention, the method described in claim 1 is carried out. In addition, the invention is carried out in a node and a program unit as described in claims 13 and 15. Embodiments

Advantageous are described in other claims.

The proposed method refers to a communication network comprising a plurality of interconnected nodes. In the communication network, a phased connection is established between nodes, usually with an establishment message or

15 a group of establishment messages. At least two of the nodes are adapted to insert an entity in the connection that affects the quality of the connection or eliminates an entity that affects the connection quality of the connection. The entity can be performed as hardware or as software executed in a node treatment system.

An indicator is transmitted between the nodes that control the connection, preferably until a final node that controls the connection or a last node that can handle the indicator is reached. The indicator indicates whether an entity that affects the quality of the connection is present in the connection or, if the connection has not been fully established, in the part of the connection already established. The indicator

25 may for example be sent in the establishment message. A node that controls the connection is adapted to insert an entity in the connection or remove an entity from it, optionally by means of control messages to other nodes. If the control node decides to insert or delete a transcoder, the node adjusts the indicator accordingly, transmitting the

30 indicator set to another node that controls the connection.

In a decision to insert or delete an entity during connection establishment or modifications, a node that controls the connection can then check the value of the indicator. The decision can be activated for example by a request to modify the connection parameters of another node or at the node itself, for example if a delivery is necessary. For example, the result of the decision may be to add a transcoder if the indicator indicates that there are no transcoders in the connection while preferably no transcoders are added if other transcoders already exist. The elimination of a transcoder is caused if a node of the connection receives a request to modify the coding scheme in a section of the connection to the coding scheme that is already used in the adjacent section on the other side of said node while a Preferable node compares the coding schemes in both adjacent sections and eliminates unnecessary transcoders.

The proposed method is specially adapted for out-of-band signaling for the establishment and modification of the connection. It is, however, also applicable for connections with in-band signaling. In the latter case, the connection is preferably established in the first stage, the presence of entities that affect the quality and the indicator are determined in a second stage and finally modifications of the entities can be carried out to reach the desired value. of the indicator.

The proposed method allows to improve the average quality of the connections in a communication network and avoid the deterioration of a connection due to changes in the coding scheme. The impacts on the connection in the core network are minimized because many modifications can remain local on a single node or on a pair of adjacent nodes. It is possible to make temporary modifications, especially when they are located within a node, without sending an indicator, for example an insertion of a pair of transcoders of the connection for an announcement or tone insertion.

In a preferred embodiment, the indicator is a flag indicating whether an entity is present in the connection. This allows a simple implementation of the method and a small message size.

Alternatively, the indicator may be a counter indicating the number of entities in the connection. The indicator can also be a variable that indicates the degradation of conversation accumulated by the entities of the connection. For the evaluation of the indicator in the decision, a comparison with a threshold value is proposed. This allows another transcoder to be inserted even if the connection already comprises one although a number of transcoders or a conversation degradation greater than the threshold is excluded. The connection control improves in this way.

The entity that affects the quality of the conversation can especially be a transcoder or a pair of transcoders. Another example is a conference device for connecting conference calls.

The management and control of the connection can be carried out on the same node, for example in a mobile telephone service switching center according to the GSM specifications. Alternatively, the communication network may comprise a separate control plane that controls nodes and a user plane with payload nodes that are controlled by the control nodes. Then control messages, for example setting messages, comprising the indicator are sent between the control nodes and the connection is established between the payload nodes.

The proposed method is especially suitable if the connection is a conversation connection.

In a modification of the connection, the insertion or deletion of entities is preferably controlled by modification messages between the nodes that control the connection.

To provide the current value of the indicator to the nodes that control the connection, the indicator can be included in an establishment message or in a modification message. Preferably, the result of all changes during the establishment or modification of a connection, that is the final value of the indicator, is transmitted to the nodes that control the connection, especially to the nodes adapted to insert or delete an entity. The indicator can be updated in a recognition message for a modification message or an establishment message, respectively.

To resolve conflicts in the case of cross-modification messages, it is proposed that a defined node that controls the connection has a priority to select a modification. For example, either the start node or the end node of any connection may have the priority to eliminate modifications by other nodes in this case.

A preferable node for controlling a connection in a communication network with a plurality of nodes has an interface with at least one other node to receive control messages for a connection, for example establishment messages, modification messages or acknowledgments. A node processing system is adapted to establish at least one section of the connection and insert an entity in the connection that affects the quality of the connection or eliminate an entity that affects the connection quality of the connection. If the node is a control node, these processes can be carried out by corresponding orders to a payload node.

The proposed node treatment system checks a control message received for an indicator indicating the presence of an entity that affects the quality of the connection in the connection and stores the value of the indicator in a memory. The treatment system checks the current value of the indicator when it makes a decision to insert or delete an entity. The treatment system adjusts the value of the stored indicator according to the decision and transmits the value on the interface to another node of the connection. The node can be used in any of the previous methods.

An advantageous program unit is stored in a data carrier

or loadable on a network node and comprises a code for receiving a control message for a connection, for example an establishment message or a modification message or an acknowledgment message. The program unit checks the message received for an indicator that indicates the presence of an entity that affects the connection quality of the connection. The unit evaluates the indicator in a decision to insert or delete an entity that affects the quality of the connection, adapts the indicator according to the decision and sends it in a message to another node that controls the connection. The program unit initiates the insertion of the entity according to the decision.

Functions of the program unit can be carried out by means of function calls to other program units, for example to a treatment system. The program unit can carry out stages from any of the above methods.

The foregoing and other objects, features and advantages of the present invention will become more apparent in the following detailed description of preferred embodiments as illustrated in the accompanying drawings.

Brief description of the drawings

Fig. 1 shows the establishment of a first connection in a network of

communication.

Fig. 2

shows the establishment of a second connection in a network of

communication.

Fig. 3

shows the establishment of a connection with a transcoder in the

border between two core networks.

Fig. 4

shows the establishment of a connection with a transit network between two

core networks

Fig. 5

shows a first alternative for the connection shown in figure 1

After a delivery.

Fig. 6

shows a second alternative for the connection shown in figure 1

After a delivery.

Fig. 7 shows a connection corresponding to figure 4 after a delivery. Fig. 8 shows the establishment and modification of a connection according to the

invention.

Fig. 9

shows the establishment of a connection according to another embodiment of

the invention.

Fig. 10

shows a modification of the connection of Fig. 9 after a delivery.

Fig. 11

shows a flow chart on a control node according to the

invention.

Fig. 12

shows a flow chart on a start control node according to the

invention.

Detailed description of preferred embodiments of the invention

In the following description, Figures 1 to 4 show different examples of connections. Figures 5 to 7 represent the influences of modifications on these connections without the proposed method while Figures 8 to 10 illustrate the influences of modifications carried out using the proposed method. Corresponding reference signs refer to corresponding characteristics in all figures.

Figure 1 shows the establishment of a first connection in a communication network. The network comprises a user plane with MG payload nodes, for example media gateways, for handling the payload. At both ends, the RAN access nodes provide connections to UMTS radio access networks that handle wireless connections with the user equipment. A control plane comprises control nodes, for example Mobile services Switching Centers (MSC) and TSN transit nodes, which control the MG nodes that handle the payload. It is possible that a control node controls several payload nodes or that a payload node is controlled by several control nodes simultaneously.

The connection establishment is initiated from a starting MSC control node, for example according to a call request from a user equipment via the RAN access network. The connection is established in stages using one or more messages sent between the control nodes that control the nodes that handle the payload in the following sections of the CO connection. The messages comprise a CL list of possible coding schemes for the connection that can be selected by a receiving node. A list of typical coding schemes includes, for example, the AMR (Adaptive Multirate Coding), EFR (Enhanced Full Rate) and PCM schemes also denoted by G711. The receiving node returns an SC acknowledgment message with the selected coding scheme indicated in quotes. In the example, AMR encoding can be selected for the entire connection because all nodes are compatible with UMTS specifications.

The connection of Figure 1 is established between two PLMN networks of UMTS CN1, CN2 as indicated by a dotted line that separates both. The mode of transport in the user plane of the two networks is for example ATM. When the connection is established from the RAN access node and all nodes select AMR for the connection, this encoding scheme can be used end-to-end between the two RAN access nodes, RAN 'through the two core networks CN1, CN2.

For simplicity, as in all the figures, the connections represented by dashed lines indicate a coding scheme with conversation compression while the solid lines indicate a coding scheme without conversation compression. The black rectangles represent a TR transcoder in the respective node.

The coding scheme negotiation procedures allow a node to insert a modification if it cannot continue to establish the connection using a compressed vos coding scheme from the available CL list. In a second connection shown in Figure 2, the source RAN access node is again part of a UMTS radio access network while the receiving end is a GSM network with a base station controller as a network of BSC access for connection to a CN2 core network. As in Figure 1, the AMR coding scheme can be used through most of the connection.

However, at the receiving end it is necessary to include a transcoder to convert the PCM type coding scheme required by the Base Station Controller BSC ’(Base Station Controller).

Different scenarios with a transcoder TR ', TR "at the border between two core networks are shown in Figures 3 and 4. In Figure 3, the termination user is located in a PSTN CNF (Public Switched Telephone Network - Red Public Switched Telephone) with a Local Exchange (LE - Central Local) as a control node and connected to a SUB access network. In the PSTN, the selected coding scheme is G711 while in the PLMN CN1 serving the startup user, the selected coding scheme is AMR. This requires the insertion of a TR ’transcoder at the border of the two networks. As this is the only transcoder in the connection, the quality of the conversation is sufficient.

In the example of Figure 4, the start user is served by a UMTS core network with a RAN access node while the end user is serviced by a GSM network with BSC access node. Both networks are interconnected by a TNN transit network that does not support compressed voice transmission, but that transmits a CT establishment message and transfers an ST recognition message. In this case the start end receives an AMR coding scheme while the connection end end requires a G711 coding scheme. Another transcoding is required for the TNN transit network which may be for example an STM network that requires PCM coding. Corresponding TR ”transcoders are located at the edges indicated by dashed and dotted lines between core networks CN1, TNN, CN2. The result is that the high number of four transcoding stages causes a significant degradation of the connection quality.

It is often necessary to modify the coding scheme in a section of a connection, for example if the connection is transferred between different access networks due to the delivery that may be required when a user leaves a coverage area of a network or if You need a different access network to meet the changed connection requirements. As can be seen from Figures 5 to 7 there are generally two options if a modification is necessary for coding in a section of a connection.

one.

A modification of the coding scheme can be carried out and indicated, resulting in the modification either in a different compressed voice coding scheme (<16 kb / s) or in a non-compressed PCM coding (Pulse Code Modulation - Modulation of Pulse Code) (64 kb / s).

2.

Two transcoders can be inserted, one to adapt to the active coding scheme of the transmission section and the other to adapt to the new coding scheme after modification. PCM coding takes place between the transcoders. If the transcoders are located together only a very short section of the transmission is carried out at 64 kb / s, ideally within a node.

If the first option is carried out and there is no transcoder in the connection as in the example of Figure 1, then the BICC coding scheme modification procedures cause a transcoder to be inserted into the access node of the furthest end . This is what the coding scheme modification procedures will end because any intermediate node that receives an MC code modification message carries out the modification and sends the message to the subsequent node until a node that cannot transmit it is reached. Thus the entire connection through core networks reverts to PCM with a data rate of 64 kb / s which is confirmed in an MCA acknowledgment message returned to the node that initiated the modification. Modification is often disadvantageous since more bandwidth is needed in the network and modifications are necessary on all nodes. Two modifications are added to the connection as can be seen from the comparison of Figures 1 and 5.

If a re-negotiation of the connection with a new list of coding schemes is allowed in the network, the result may be an encoding that was not negotiated in the establishment of the connection, for example the modified coding scheme is not contained in the list of GSM coding schemes to support TFO. Then there may be a node in the connection that does not support the coding scheme. As a result, it would also be necessary to use PCM over the network.

The second of the above options is advantageous if the entire connection was originally without transcoders because only transcoders are added that are preferably located in the same access network or in an access node and a node adjacent to the access network that requires modification. . No modifications to other sections of the connection or other connection nodes are necessary. This saves bandwidth and also avoids the complications of inserting transcoders at the far end of the connection. This is obvious from the comparison of Figures 5 and 6.

However, the second option is not the best solution if the connection was already established with transcoders in other parts of the network as in Figure 4. This results in six transcoders in the example of Figure 7 that severely affect quality. of the connection. In contrast, a modification of the coding scheme according to the first option would eliminate a transcoder in the example of Figure 4. In the example of Figure 3, the second option would also increase the number of transcoders.

A problem with existing connection control messages is that the connection nodes do not know if the connection was successfully negotiated end-to-end with a single coding scheme or if a transcoder is inserted, for example when the connection crosses the border between networks. The proposed method provides information to the nodes that carry out the negotiation of the coding scheme about the transcoding steps in the connection. The node can then optimize the establishment or the modifications in the coding of the connection both for the use of bandwidth and for the transcoding steps, that is to say the node can select the preferable one of the two previous options.

The method proposes a new indicator that is, for example, added to the message in the negotiation of the connection parameters according to BICC. The indicator can be implemented in several different ways. Two embodiments are a flag indicating whether a connection is free of end-to-end transcoders or a counter that contains the number of transcoders in a connection.

It is possible that the connection is modified in two nodes, for example in the case of a delivery at both ends of a connection or an introduction of a supplementary service and a delivery. In this case, the indicator is not sufficient to achieve the desired transcoder configuration. For example, nodes at both ends of a connection can add a pair of transcoders that result in four transcoders. This can be avoided by a CM Code Modification message sent to all control nodes of the connection comprising the indicator or indicating that the indicator has changed. The control nodes MSC, TSN for the access and payload nodes are thus always provided with the current state of the flag or transcoder counter of the connection. A problem may occur in the case of a cross event when both sides modify the connection and correspondingly the indicator almost simultaneously, that is, the indicator is not adapted by the CM code modification message fast enough to represent the current state of the Connection. To solve this problem, an MCA recognition is proposed. Preferably, the MCA recognition also includes the current status of the indicator. One side of the connection, for example the start side has a higher priority to insert transcoders. The side with a higher priority can then reject the change of the side with lower priority or only the side with lower priority modifies the coding.

In the first embodiment, the indicator is a TF flag indicating whether the negotiation of the coding scheme for the establishment of a connection or a modification was carried out end to end or terminated at an intermediate node of the network. This provides the necessary information to the nodes of the connection, for example the control node for an access network, to decide whether another one or two transcoders can add in a connection. If this is the case, the access node and the adjacent payload node add a pair of transcoders if the flag is not set while no transcoder

or a single transcoder are added if the flag is adjusted. For example, in the case of a delivery from a UMTS access network to a GSM network, the UMTS AMR can be maintained in a PLMN as shown in Figure 8. This saves bandwidth in the core network and prevents unnecessary modifications of the connection. An advantage of the realization of the flag indicator is that a single bit is sufficient to represent the possible "and" states corresponding to a connection without end-to-end transcoders and "n" corresponding to a connection comprising transcoders. The implementation is simple.

In the second embodiment, the indicator is a counter that represents the number of transcoding steps that are passed between nodes during connection establishment and changes in the transcoder. This allows the application of a threshold for the number of transcoding stages that can be inserted. More generally, the method can also be applied to avoid the degradation of the conversation due to other equipment in the connection that affects the quality of the conversation. The maximum number of stages depends on the level by which the connection is affected at each stage. A suitable threshold value is, for example, three transcoding steps as a maximum allowed value. The threshold can also depend on the coding scheme selected in a section, for example the threshold can be three stages except when the EFR coding is selected for which a maximum of four stages could be allowed. In a third embodiment, it is also possible that instead of a counter representing the number of stages, the indicator is a variable that is increased according to the level of degradation caused by the respective stage.

When a connection with BICC messages is established, the APP sent at the sending address includes the indicator and the indicator is incremented if a node inserts a transcoder unit. The termination node receives the indicator and determines if it can still add transcoders. If the termination node inserts a transcoder, it also increases the counter. From the termination node, the counter is returned to the start node in the APM (Application Transport Mechanism) together with the selected coding scheme. The value is stored in all the nodes that control the connection. If a modification takes place, for example due to a delivery, the transcoder counter is updated and sent with the APM for the modification of the coding scheme to all control nodes for the connection.

If a network node initiates the negotiation of the coding scheme for a connection from a network in which the transcoder counter is not supported (for example, in which BICC is not supported or in which a flag is used instead of a transcoder counter) preferably a default value corresponding to an unknown number of transcoding stage is set.

Figure 9 represents the establishment of a connection in a communication network as described with respect to Figure 4. The MSC has received AMR as the coding scheme selected in the message SC, and thus compressed conversation is used through the core network CN1. In this case, the TNN transit network is adapted to transmit the indicator, that is to say the TN transcoder counter, in a CT message and in the corresponding ST recognition. Therefore, all connection control nodes are provided by the acknowledgment messages SC, SC ’, ST with the information that two transcoders are linked in the connection.

In Figure 10, a HandOver (HO-delivery) for this connection is carried out from a UMTS RAN access node to a GSM BSC access node. The MSC anchor node for HO delivery has stored the counter indicating that the connection already has two transcoders in it. If two other transcoders are added in the access section of the connection then the threshold for the number of transcoders will be exceeded. Therefore, a single transcoder is added to the BSC access node as delivery requires resulting in a current number of transcoders of three in the connection. The decision is then taken at the MSC control node to modify the coding scheme for PCM which generally reduces the number of transcoders in a connection to a maximum of two because all the nodes in the core networks can handle the coding scheme. of PCM. The information passed to the next control node in the MC code modification message with the current value of the counter of three. The message to modify the PCM coding scheme, which is already used in a section of the connection adjacent to the payload node MG ', also in the other section adjacent to the payload node MG' allows the control node TSN delete the transcoder unit at the border of the network. The updated TN transcoder counter of two is then returned to the MSC control node in the MCA recognition. Preferably, the updated TN transcoder counter is also sent to other TSN ’, MSC’ control nodes in connection with MCA ’, MCA messages.”

The same decision can also be made if the counter is not supported by the transit node or set to a default value by the TSN transit node. Then the anchor point MSC makes the same decision based on the fact that an unknown number of transcoders is present in the connection.

In both the case of Figure 9 and that of Figure 10, the first MSC control node could receive a high number of transcoders in the SC, MCA recognition messages, depending on the selections of the other TSN control nodes, TSN ', MSC' in the connection and network architecture. In this case, the first MSC control node can modify the connection with another code transcoder message to reduce the number of transcoders.

Figure 11 represents an example of a flowchart for the decision to insert a transcoder into a traffic control or termination node MSC, TSN for a connection, for example in a node receiving an establishment message 2. In the message 2, the control node receives a CL list with allowed coding schemes and the TC counter with the number of transcoders of the connection. The node checks if all coding schemes in the CL list are supported and removes unsupported schemes in step 4. Then a check 6 is carried out of whether a transcoder is needed or preferably, for example because the node is located at a border between core networks or an access network with different transport protocols.

If the result of the check 6 is that a transcoder must be inserted, the TC counter is incremented in step 8 and a comparison 10 of the transcoder counter is performed with a predefined threshold for the maximum number of transcoders. If the result of comparison 10 is that the number of transcoders is equal to or greater than the threshold, G711 is selected as the coding scheme in step 12 and the transcoder counter is decreased. Next, another check 14 is carried out on whether the node is an end node that controls the connection or the transit node. In the case of a transit node, the CL list of allowed coding schemes is reduced to G711 in step 16. The reduced CL list consisting only of G711 as the only allowed coding scheme is sent together with the updated TC transcoder counter to the next control node for connection in another setup message 18.

The result of the check 14 may also be that the control node is an end node, for example the last control node before the connection termination access network. Next, a transmission of the selected coding scheme is carried out, that is to say G711, together with the number of transcoders to the connection initiation node by means of all the transit nodes in a message 20.

If no transcoder is required as determined in check 6 or if the number of transcoders is lower than the threshold as determined in check 10, then a check 22 is also carried out if the node is the termination node that Control the connection. For a termination node, a selection 24 of a coding scheme of the CL list is carried out. As an insert 26 of one or a pair of transcoders is performed if a transcoder is required as determined in check 6. The coding scheme selected from check 22 and the final value of the transcoder counter TC it is returned in a message 20 to the start node by means of all transit nodes.

For a transit node according to check 22, the adjusted CL list of coding schemes and the value of the transcoder counter TC are transmitted to the next control node for connection in a message 18. Preferably, the insertion of the transcoders in the connection it is carried out in accordance with the coding scheme selected in an encoding scheme in a recognition message that is received in response to message 18.

Figure 12 represents a corresponding flowchart for a start control node in a connection. In a first stage 40, the counter of 5 transcoders TC is set to zero. A decision 42 is then taken as to whether a transcoder is needed or is preferable, for example because the local insertion of a transcoder prevents the modification of the transcoder in another section of the connection. If the decision 42 is to insert a transcoder, the counter is incremented in step 44. A CL list of allowed coding schemes is defined in step 46, depending on the capabilities of the start node. Finally, a message 48 comprising a list CL and the value of the counter TC is transmitted in a message to the next control node for the connection. Depending on the implementation, the insertion of a transcoder can for example be carried out in step 44 or when an acknowledgment to message 48 is received with a

15 coding scheme selected from the CL list.

The proposed method allows the nodes to optimize transcoder insertion, especially when using out-of-band coding scheme negotiation mechanisms. It will be appreciated that the scope of the invention is limited only to the claims.

twenty

Claims (15)

1. Method for controlling a connection in a communication network comprising a plurality of nodes (MSC, TSN, MG), in which a connection (CO) is established in stages between nodes (MSC, TSN, MG) and at least two of the nodes (MSC, TSN, MG) are adapted to insert an entity in the connection (CO), affecting the entity to the quality of the connection, or to eliminate an entity that affects the quality of the connection the connection, in which an indicator is sent between the nodes that control the connection (CO) in which the indicator indicates whether the connection (CO) comprises an entity that affects the quality of the connection, a node that decides to insert an entity in the connection or delete an entity adjusts the indicator accordingly, before sending it to another node (MSC, TSN, MSC ’) that controls the connection (CO), and a node (MSC, TSN, MSC ’) that controls the connection (CO) checks the value of the indicator when it makes a decision to insert or delete an entity.

2.

Method according to claim 1, wherein the indicator is a flag (TF) indicating if any entity is present in the connection.

3.

Method according to claim 1, wherein the indicator is a counter (TN) indicating the number of connection entities.

Four.

Method according to claim 1, wherein the indicator is a variable indicating the degradation of the conversation accumulated by the entities of the connection.

5.

Method according to claim 3 or 4, wherein the indicator is compared with a threshold value in the decision.

6.

Method according to any preceding claim, wherein an entity is a transcoder (TR) or a conference device.

7.

Method according to any preceding claim, wherein a communication network comprises control nodes (MSC, TSN) and load nodes

useful (MG) that is controlled by the control nodes (MSC, TSN), in which the indicator is sent between control nodes (MSC, TSN) and the connection (CO) is established between the payload nodes (MG ).

8.

Method according to any preceding claim, wherein the connection (CO) is a conversation connection.

9.

Method according to any preceding claim, in which an entity is inserted or deleted according to a modification message (MC).

10.

Method according to any preceding claim, wherein the indicator is sent with an establishment message for connection (CO) or a modification message (MC) or an acknowledgment (MCA, SC) of a modification message or a message of establishment.

eleven.

Method according to any preceding claim, wherein a final value of the indicator after the establishment or modification of the connection (CO) is transmitted to nodes (MSC, TSN) in the connection that are adapted to insert

or delete an entity.

12.

Method according to any preceding claim, wherein a defined node (MSC) that controls the connection has a priority to select a modification.

13.

Node for the control of a connection in a communication network comprising a plurality of nodes (MSC, TSN, MG), in which the node (MSC, TSN) has an interface to at least one other node (MSC, TSN) for receive control messages for the connection (CO) and has a treatment system adapted to establish at least one section of the connection (CO) and insert an entity in the connection that affects the quality of the connection or eliminate an entity that affects to the connection quality of the connection, in which

The treatment system is adapted to extract an indicator from a control message, indicating the indicator if an entity that affects quality is present in the connection (CO), The treatment system comprises a memory for storing the indicator value, the treatment system checks the value of the indicator when the decision is made to insert or delete an entity and the treatment system adjusts the value of the stored indicator according to the decision and sends the value over the interface to another node of the connection (CO). The node according to claim 13 adapted to carry out a method according to one of claims 2 to 12. 15. Program unit on a data carrier or loadable on a network node, the program unit comprising a code for carrying out the steps of 10 Receive a control message (MS, MCA, SC) for a connection that checks the received message (MC, MCA, SC) for an indicator that indicates whether an entity that affects the quality of the connection is present in the connection ( CO), Evaluate the indicator in a decision to insert or remove an entity that affects the quality of the connection (CO), 15 Adapt the indicator according to the decision and send it in a control message to another node of the connection (CO), Start the insertion or deletion of the entity according to the decision. 16. Program unit according to claim 15, wherein the Program unit is adapted to carry out a method according to any one of claims 2 to 12.